Almost all time limits for assessment of tax were decreased earlier by three months . So , A.Os had time for assessment of tax up to December of the year concerned. This lowering of time to complete assessment under various provisions under Income Tax Act was done with the intention of the tax administrator that the Assessing Officer will devote the three months of a fiscal year in collection work.
It is already posted elsewhere in the blog that if one claims deduction u/s 80C, then one should not sell the ULIP units before five years of holding . If one does that the deduction allowed shall be taken as income of the year in which you sell. Readers are advised to read What You Must Know About Tax Impact on Surrender of Insurance Policy?